What Tire Size?

**schrysler** · 08-01-2007, 10:58 AM

I have found a killer deal on some rims and am looking for some tires, question is what would be the best tire sizes for 18x9.5 in back and 18x8.5 in the front? The back is a no brainer for me either 275/35/18 or 295/35/18 but the front is where i am getting stuck, why do people do 245/40/18 in the front instead of keeping it 35?

**Jays00ss** · 08-01-2007, 11:49 AM

it stays true to the stock diameter.

**schrysler** · 08-01-2007, 02:24 PM

BUT THE FRONT AND THE BACK ARE 18's isnt the 35 or 40 the amount of side wall? I would think that it would look weird having two different size sidewalls on the same car.

**mrr23** · 08-01-2007, 03:17 PM

Originally Posted by schrysler

BUT THE FRONT AND THE BACK ARE 18's isnt the 35 or 40 the amount of side wall? I would think that it would look weird having two different size sidewalls on the same car.

sidewall height is determined by width. that 40 is a percentage number. 40% of 245mm gives you the sidewall height.

i give tire sizes that are equivalent to factory tire diameter in the sticky above.

http://www.ls1.com/forums/showthread.php?t=11359

the 245/40-18 and the 275/35-18 have the same amount of sidewall. both on 18" wheels and both are 25.7" tall.

**Talenuf** · 08-02-2007, 08:17 PM

Somewhere here is a chart of acceptable tire sizes for given wheel widths. Can somebody drop the link to that here? Thanks!

**Eugenio_SS** · 08-09-2007, 10:30 PM

to calculate overall diameter... it's as follows:
let's understand the #s.
example : 275/40-17

means
275: width of tire = 275mm
40: sidewall is 40% of 275mm = 275 x 0.40 = 110mm = 4.33" (note: 1" = 25.4mm)
17: size of wheel = 17"

Overall diameter = size of wheel + 2 sidewalls (the top and the bottom)
OD = 17" + 2x4.33" = 25.66"

so if we take 245/40-18
sidewall: 245x0.4 = 98mm = 3.86"
OD: 18" + 2x3.86" = 25.72"

275/35-18
sidewall: 275x0.35 = 96.25mm = 3.79"
OD: 18" + 2x3.79" = 25.58"

Hope this helps.